Abstract

It is well known that birds and air vehicles are capable of extracting energy from atmospheric winds. Land birds such as condors and vultures remain aloft for hours at a time without flapping their wings. In straight and level flight, atmospheric wind updrafts rotate the relative aerodynamic velocity vector downward, causing the drag to point aft and slightly upward and the lift to point up and slightly forward. When the atmospheric wind updraft is sufficiently large, straight and level flight and even climbing flight are possible without power. Conventional sailplane soaring is based on this type of atmospheric wind energy extraction. Autonomous soaring has also been well researched, including flight-test experiments. It is known for a long time that sea birds such as albatrosses and petrels are capable of extended flight over the sea without flapping their wings. However, the physical mechanism in this case is fundamentally different from land birds. Seabirds extract energy from an atmospheric wind gradient near the surface of the ocean by alternating climbing and diving upwind and downwind of air masses moving at differing velocities. This type of atmospheric wind energy extraction is known as dynamic soaring and has been studied by a number of researchers, particularly for remote-control gliders flying near ridges.